In Chess illegal moves can never occur in a game; FIDE rules prescribe that such move should be taken back, and replaced by a legal one. But in Shogi, you just lose.
I checked Wikipedia, and it says the following:
In professional and serious (tournament) amateur games, a player who makes an illegal move loses immediately.[c] The loss stands even if play continued and the move was discovered later in game. However, if neither the opponent nor a third party points out the illegal move and the opponent later resigned, the resignation stands as the result.
This makes sense for over-the-board games, which is how Shogi is normally played in professional tournaments. But it does not make sense for Game Courier, which lets players preview their moves before confirming them. Just like it makes sense for Game Courier to ignore the rule in Chess that you have to move a piece if you touch it, it makes sense for Game Courier to ignore this rule.
The Japanese consider this an important thing: the 81-Dojo server does not refuse illegal Pawn drops, because that would be considered computer help.
I have never played on that server. Given the way this Game Courier preset works, each side is provided computer help, but it is equal for each player. If players want to play without computer help, as players in over-the-board tournaments do, they can play an unprogrammed preset. The programmed preset is programmed to display legal moves and forbid illegal moves, and to do this consistently, it should display only legal moves as legal and forbid all illegal moves.
I checked Wikipedia, and it says the following:
This makes sense for over-the-board games, which is how Shogi is normally played in professional tournaments. But it does not make sense for Game Courier, which lets players preview their moves before confirming them. Just like it makes sense for Game Courier to ignore the rule in Chess that you have to move a piece if you touch it, it makes sense for Game Courier to ignore this rule.
I have never played on that server. Given the way this Game Courier preset works, each side is provided computer help, but it is equal for each player. If players want to play without computer help, as players in over-the-board tournaments do, they can play an unprogrammed preset. The programmed preset is programmed to display legal moves and forbid illegal moves, and to do this consistently, it should display only legal moves as legal and forbid all illegal moves.